AppImage is a universal software package format for all GNU/Linux distros. This format made your software "installation" extremely easier: to run GIMP for example, you just need to download one file in .appimage format, run it by few clicks, and GIMP is running. You don't need to install anything! The single .appimage file is runnable on many different distros (Ubuntu, Fedora, openSUSE, etc.). It's similar to .exe file that is compatible with any of Windows versions. The difference to Flatpak/Snappy/Alldeb solution is AppImage requires no additional program installed. It sounds interesting, no? So here how to run one .appimage package

1. Get .appimage Package

In this March 2017, there are many free software have been already available in .appimage format. For example, the original developers of GIMP, Inkscape, Scribus, Krita, MyPaint, Chromium, and others have been packaged their software in .appimage format. It means you can download the .appimage by hand and then install it on your Ubuntu easily! For the beginning, see AppImage availability list here. In this article I use Ramme appimage file (an Instagram client for GNU/Linux) for 64-bit you can download here.